Aluminum brightening can be achieved either mechanically (by buffing or polishing) or chemically. "Bright dipping" is a chemical process that increases the specular reflectance (brightness) of aluminum by bathing it in acid.
Most bright dip solutions are a mixture of phosphoric acid and nitric acid with additives for extra brightening and fume suppression. Some formulations also include sulfuric acid. These chemical bright dip baths remove microscopic peaks from the aluminum surface to produce a highly specular or mirror-like finish.
Chemically polished aluminum is used in automotive trim, architectural structures, home appliances, aircraft construction, electrical components, window and door frames, shower doors, picture frames, cosmetic containers, surgical instruments, any many other products.
PotashCorp Aluminum Brightening products